Metabolic adaptation to vitamin auxotrophy by leaf-associated bacteria

Auxotrophs are unable to synthesize all the metabolites essential for their metabolism and rely on others to provide them. They have been intensively studied in laboratory-generated and -evolved mutants, but emergent adaptation mechanisms to auxotrophy have not been systematically addressed. Here, we investigated auxotrophies in bacteria isolated from Arabidopsis thaliana leaves and found that up to half of the strains have auxotrophic requirements for biotin, niacin, pantothenate and/or thiamine. We then explored the genetic basis of auxotrophy as well as traits that co-occurred with vitamin auxotrophy. We found that auxotrophic strains generally stored coenzymes with the capacity to grow exponentially for 1-3 doublings without vitamin supplementation; however, the highest observed storage was for biotin, which allowed for 9 doublings in one strain. In co-culture experiments, we demonstrated vitamin supply to auxotrophs, and found that auxotrophic strains maintained higher species richness than prototrophs upon external supplementation with vitamins. Extension of a consumer-resource model predicted that auxotrophs can utilize carbon compounds provided by other organisms, suggesting that auxotrophic strains benefit from metabolic by-products beyond vitamins.

Automated summary

Auxotrophs are organisms that cannot synthesize all the essential metabolites and rely on others for their survival. In a study of bacteria isolated from Arabidopsis thaliana leaves, it was found that about half of the strains require biotin, niacin, pantothenate, and/or thiamine. These auxotrophic strains were able to store coenzymes and grow exponentially for a few generations without vitamin supplementation, with biotin showing the highest storage capacity. Co-culture experiments showed that auxotrophic strains had higher species richness when provided with external vitamins. The results suggest that auxotrophs can benefit from metabolic by-products beyond vitamins.